Transmission control system for a vehicle

ABSTRACT

A CVT controller  22  of a vehicle  10  communicates with the engine management system (EMS)  20.  When a manual shift between simulated fixed ratios is performed, the CVT controller  22  sends a shift signal to the EMS  20  which alters the engine torque for the duration of the shift in order to simulate a manual shift to provide, for example, a sporty feel to the vehicle  10.

FIELD OF THE INVENTION

This invention relates to transmission control systems for vehicles andin particular to a transmission control system for a continuouslyvariable transmission suitable for use in a vehicle; to a method ofcontrolling such a transmission control system; and to a vehicle havingsuch a transmission control system.

BACKGROUND OF THE INVENTION

It is known to control a continuously variable transmission (CVT) byoperating an associated prime mover at its optimum efficiency and bycontinually varying the output ratio of the transmission to fulfill thedemands for torque output placed on the powertrain. It is an object ofthe control systems for some known CVTs to provide a smooth output fromthe transmission throughout the operating range of the powertrain.

When such a CVT is fitted to a vehicle, it is usually the aim of thedesigner to ensure that the CVT has as smooth a torque output aspossible. In this way, a user experiences a power delivery which isrefined and seamless, i.e. devoid of step changes. One such prior artsystem is disclosed in U.S. Pat. No. 4,653,005.

For some applications, however, it is desirable to provide noticeablechanges in powertrain output, in order to provide powertrain feedback tothe user. For example, in a sports car it is often perceived that thedriving experience should involve feedback from the powertrain at pointsin the power delivery which would simulate drops and/or surges in torquearound gear shifts and thus be reminiscent of the manual gear shiftsbeloved of some users of traditional or classic sports cars.

It is an object of this invention to provide: an improved transmissioncontrol system for a continuously variable transmission suitable for usein a vehicle; a method of controlling such an improved transmissioncontrol system; and to provide a vehicle having such an improvedtransmission control system.

SUMMARY OF THE INVENTION

According to the invention there is provided a transmission controlsystem for a vehicle comprising a prime mover control means arranged inuse to control the torque output from a prime mover and a transmissioncontrol means arranged in use to control a continuously variabletransmission so as to operate in a plurality of substantially discreteratios and to control shifts between said ratios, characterised in thatthe transmission control means is arranged to provide a shift signal tothe prime mover control means indicative of a shift between said ratiosand the prime mover control means is arranged to temporarily alter saidtorque output in response to said shift signal, whereby in use a user isprovided with feedback which is indicative of said shift and which is inthe form of a substantially stepped change in said torque output.

The prime mover control means may be arranged to alter said torqueoutput by reducing it and may be arranged to raise said torque output atthe end of a shift between said ratios.

The prime mover control means may be arranged to alter said torqueoutput by increasing it and may be arranged to reduce said torque outputat the end of a shift between said ratios.

The prime mover control means may be arranged to alter said torqueoutput substantially for the duration of each shift between said ratios.

The transmission control means may comprise a manual input means formanual selection of shifts between said ratios.

The prime mover may comprise an engine and the prime mover control meansmay be arranged to alter said torque output by varying the supply offuel to a cylinder of said engine.

The prime mover may comprise a spark ignition engine and the prime movercontrol means may be arranged to alter said torque output by varying theignition timing of said engine.

The prime mover may comprise an engine and the prime mover control meansmay be arranged to alter said torque output by varying the supply of airto a cylinder of said engine.

The prime mover may comprise an electrical machine and the prime movercontrol means may be arranged to alter said torque output by varying anelectrical supply of said electrical machine.

The invention also provides a vehicle having a transmission controlsystem according to the invention.

The invention also provides a method of controlling a transmissioncontrol system for a vehicle comprising a prime mover control meansarranged in use to control the torque output from a prime mover and atransmission control means arranged in use to control a continuouslyvariable transmission so as to operate in a plurality of substantiallydiscrete ratios and to control shifts between said ratios, characterizedin that the method includes the steps of:

a) providing a shift signal from the transmission control means to theprime mover control means indicative of a shift between said ratios; and

b) altering temporarily said torque output in response to said shiftsignal;

whereby in use a user is provided with feedback which is indicative ofsaid shift and which is in the form of a substantially stepped change insaid torque output.

The method may include altering said torque output by reducing it andmay include raising said torque output at the end of a shift betweensaid ratios.

The method may include altering said torque output by increasing it andmay include reducing said torque output at the end of a shift betweensaid ratios.

The method may include altering said torque output substantially for theduration of each shift between said ratios.

The method may include manually selecting shifts between said ratiosusing a manual input means comprising part of the transmission controlmeans.

The prime mover may comprise an engine and the method may includealtering said torque output by varying the supply of fuel to a cylinderof said engine.

The prime mover may comprise a spark ignition engine and the method mayinclude altering said torque output by varying the ignition timing ofsaid engine.

The prime mover may comprise an engine and the method may includealtering said torque output by varying the supply of air to a cylinderof said engine.

The prime mover may comprise an electrical machine and the method mayinclude altering said torque output by varying an electrical supply ofsaid electrical machine.

BRIEF DESCRIPTION OF THE DRAWING(S)

The invention will now be described by way of example with reference tothe accompanying drawing, in which:

FIG. 1 is a schematic diagram of a vehicle having a transmission controlsystem according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to the figure, a vehicle 10 comprises a prime mover in theform of a spark ignition engine 12 connected to a continuously variabletransmission (CVT) 14 which provides drive to a set of wheels 16.

The engine 12 and the CVT 14 are controlled by a combined powertraincontroller 18, comprising an engine management system (EMS) 20 and a CVTcontroller 22 which communicate with each other.

The engine 12 has an ignition system 24 and a fueling system comprisinga fuel injection means 26 and a throttle butterfly 28 driven by a motor30, all under the control of the EMS 20 to regulate the torque output ofthe engine 12. The CVT 14 has a shift mechanism 32, which is under thecontrol of the CVT controller 22, to control its output to the wheels16.

The vehicle 10 further comprises a transmission selector 34 having auser operated gear lever 36 which is manually slideable betweenpositions along a transmission gate 38 and which provides the CVTcontroller 22 with a signal indicating in which of the positions thegear lever 36 has been placed. The gate 38 is divided into a first track40 and a second track 42 which are interconnected by a cross track 44.

When moved along the first track 40, the selector lever 36 selectsbetween positions for; park P, reverse R, neutral N and drive D and canoperate at any ratio within its range in a conventional CVT manner. Whenin drive D, the selector lever 36 can be moved across the cross track 44and into the second track 42.

When the selector lever 36 is in the second track 42, it is springloaded to a waiting position W between an up-shift+ and a down-shift−position. The gear lever is manually moveable into the up-shift+ ordown-shift− position and returns to the waiting position W by the springloading on its release between movements.

When the selector lever 36 is moved between the up-shift+ and thedown-shift− positions, the CVT controller 22 controls the shiftmechanism 32 to operate the CVT 14 in a plurality of discrete simulatedfixed ratios and to shift up or down between them in accordance with themanual selection. The continuously variable nature of the operation ofthe CVT 14 makes it difficult to permanently fix the CVT output atspecific ratios and so the CVT controller 22 simulates fixed ratios bycontinuously adjusting the shift mechanism 32 to operate around fixedpoints of the CVT output characteristic.

On each manually selected up-shift or down-shift, initiated using theselector lever 36, the CVT controller 22 sends a shift start signal tothe EMS 20. On receipt of the shift start signal, the EMS 20 temporarilyalters the torque output of the engine 12.

The torque output is altered with time at the start of each ratio shiftand simulates the powertrain feedback the driver would experience if hewere to be operating a vehicle fitted with a manual shift mechanism,i.e. the feedback is in the form of a substantially stepped change inthe torque output, as if an accelerator pedal (not shown) were to bereleased and a clutch pedal (not shown) were to be depressed.

When the torque has been altered, the CVT controller 22 operates theshift mechanism 32 to select a higher or lower simulated fixed ratio inaccordance with the movement of the selector lever 36 along the secondtrack 42.

When the shift has been carried out, the CVT controller 22 sends a shiftend signal to the EMS 20, which then alters the torque output of theengine 12 with time so that it matches the previous setting or adopts anew setting appropriate for the newly selected transmission ratio. Thealteration of the torque output at the end of a ratio shift simulatesthe powertrain feedback the driver would experience if he were to beoperating a vehicle fitted with a manual shift mechanism, i.e. thefeedback is in the form of a substantially stepped change in the torqueoutput, as if a clutch pedal were to be released and an acceleratorpedal were to be depressed.

The torque output is altered by using one or more of three techniquesselected from a look-up table programmed in the EMS 20, the selectionbeing made in a tuneable manner depending on the instant runningconditions of the engine 12 and is further tuneable to take account ofindividual user preferences. The three methods of altering the torqueoutput are: by varying the quantity of fuel supplied to the engine 12 bythe fuel injection system 26; by the EMS 20 controlling the motor 30 topartially or fully open or close the throttle butterfly 28 and therebyvarying the supply of air to the engine 12; and by controlling theignition system 24 to vary the spark timing.

The alteration in torque output may be by its reduction, increase or amixture of these two options as preferred, in order to suit each users'perceptions of feedback for certain vehicles or under certaincircumstances.

If the torque output is reduced for a shift, it should be increased atthe end of that shift. If on the other hand the torque output is raisedfor a shift, it should be lowered at the end of that shift. In eithercase, the increase or reduction in torque output at the end of the shiftmay not be necessary, depending on the torque output demand placed onthe engine 12 by the newly selected ratio.

The alteration in torque output does not have to be limited to theduration of the ratio shift itself but may be implemented for a periodvaried in accordance with driver expectations, which would be programmedin the combined powertrain controller 18 during development testing. Thesimulation of a manual selection of ratios thus provides a sporty feelto the vehicle 10 when the selector lever 36 is operated in the secondtrack 42.

This invention could also be applied to a CVT having a conventionalcable operated throttle butterfly, rather than the drive-by-wire motoroperated butterfly 30 of the embodiment described above. The powertraincontroller could also comprise a fully integrated powertrain controllerin which the EMS 20 and the CVT controller 22 are fully integrated in asingle unit.

In a modification to the invention the prime mover comprises anelectrical machine, for example a traction motor, and the torque outputis altered by varying an electrical supply of the machine, for exampleby current control.

What is claimed is:
 1. A transmission control system for a vehiclehaving a prime mover connected to a continuously variable transmission,the prime mover supplying a torque output to the continuously variabletransmission and the continuously variable transmission receiving thetorque output from the prime mover and driving the vehicle, thetransmission control system comprising: a prime mover controllerconnected to the prime mover for controlling, during both accelerationand deceleration of the vehicle, the torque output of the prime mover;and a transmission controller connected to the continuously variabletransmission for controlling the continuously variable transmission tooperate, during operation of the vehicle, at a desired one of aplurality of substantially discrete gear ratios of the continuouslyvariable transmission and for controlling shifting of the continuouslyvariable transmission between the plurality of substantially discretegear ratios of the continuously variable transmission; wherein thetransmission controller provides a shift signal to the prime movercontroller indicative of a shift between two gear ratios of theplurality of substantially discrete gear ratios of the continuouslyvariable transmission, the prime mover controller, upon receipt of theshift signal, temporarily alters the torque output of the primer mover,and an operator of the vehicle perceives a feedback signal, indicativeof the shift between two gear ratios of the plurality of substantiallydiscrete gear ratios of the continuously variable transmission, in theform of an increased stepped change in torque output of the prime mover.2. The transmission control system according to claim 1, wherein thetransmission control system includes a manual selector which is coupledto a shift mechanism of the continuously variable transmission via thetransmission controller, the manual selector has both an upshiftposition and a downshift position, and the manual selector, when in theupshift position, facilitates an up shift of the plurality ofsubstantially discrete gear ratios of the continuously variabletransmission, and the manual selector, when in the downshift position,facilitates a down shift of the plurality of substantially discrete gearratios of the continuously variable transmission.
 3. The transmissioncontrol system according to claim 1, wherein the transmission controlsystem includes a manual selector which is coupled to the transmissioncontroller, and the feedback signal is one of a drop and a surge in thetorque output of the prime mover when the shift of each one of theplurality of substantially discrete gear ratios of the continuouslyvariable transmission occurs.
 4. The transmission control systemaccording to claim 1, wherein the prime mover controller alters thetorque output of the prime mover by reducing the torque output.
 5. Thetransmission control system according to claim 1, wherein the primemover controller alters the torque output of the prime mover byincreasing the torque output.
 6. The transmission control systemaccording to claim 1, wherein the prime mover controller alters thetorque output of the prime mover by raising the torque output at an endof a shift between the plurality of substantially discrete gear ratiosof the continuously variable transmission.
 7. The transmission controlsystem according to claim 1, wherein the prime mover controller altersthe torque output of the prime mover by reducing the torque output at anend of a shift between the plurality of substantially discrete gearratios of the continuously variable transmission.
 8. The transmissioncontrol system according to claim 1, wherein the prime mover controllerincludes a mechanism for altering the torque output of the prime moverfor an entire duration of the shift between the plurality ofsubstantially discrete gear ratios of the continuously variabletransmission.
 9. The transmission control system according to claim 1,wherein the prime mover is an engine and the prime mover controller isconnected to a butterfly valve of the engine to alter the torque outputof the prime mover by varying a supply of combustion air to the engine.10. The transmission control system according to claim 1, wherein theprime mover is an engine and the prime mover controller is connected toa fuel valve of the engine to alter the torque output of the prime moverby varying a supply of combustion fuel to the engine.
 11. Thetransmission control system according to claim 1, wherein the primemover is an engine and the prime mover controller is connected to anignition system of the engine to alter the torque output of the primemover by varying the ignition timing of the engine.
 12. The transmissioncontrol system according to claim 1, wherein the prime mover is anelectric motor and the prime mover controller is connected to anelectrical supply for the electric motor to alter the torque output ofthe electric motor by varying the supply of electricity to the electricmotor.
 13. The transmission control system according to claim 1, whereinthe transmission controller and the prime mover controller areintegrated into a combined powertrain unit.
 14. A method of controllinga transmission control system for a vehicle having a prime moverconnected to a continuously variable transmission, the prime moversupplying a torque output to the continuously variable transmission andthe continuously variable transmission receiving the torque output fromthe prime mover and driving the vehicle, the method comprising the stepsof: connecting a prime mover controller to the prime mover forcontrolling, during both acceleration and deceleration of the vehicle,the torque output of the prime mover; and connecting a transmissioncontroller to the continuously variable transmission for controlling thecontinuously variable transmission to operate, during operation of thevehicle, at a desired one of a plurality of substantially discrete gearratios of the continuously variable transmission and for controllingshifting of the continuously variable transmission between the pluralityof substantially discrete gear ratios of the continuously variabletransmission; providing, via the transmission controller, a shift signalto the prime mover controller indicative of a shift between two gearratios of the plurality of substantially discrete gear ratios of thecontinuously variable transmission, and the prime mover controller, uponreceipt of the shift signal, temporarily altering the torque output ofthe primer mover, and an operator of the vehicle perceiving a feedbacksignal, indicative of the shift between two gear ratios of the pluralityof substantially discrete gear ratios of the continuously variabletransmission, in the form of a substantially stepped change in torqueoutput of the prime mover.
 15. The method according to claim 14, furthercomprising the steps of providing the transmission control system with amanual selector coupled to a shift mechanism of the continuouslyvariable transmission via the transmission controller, the manualselector having both an upshift position and a downshift position, andthe manual selector, when in the upshift position, facilitating an upshift between two gear ratios of the plurality of substantially discretegear ratios of the continuously variable transmission, and the manualselector, when in the downshift position, facilitating a down shiftbetween two gear ratios of the plurality of substantially discrete gearratios of the continuously variable transmission.
 16. The methodaccording to claim 14, further comprising the step of providing thetransmission control system with a manual selector coupled to thetransmission controller, and the manual selector facilitating the shiftbetween two gear ratios of the plurality of substantially discrete gearratios of the continuously variable trans mission, and the feedbacksignal is one of a drop and a surge in the torque output of the primemover when the shift between two gear ratios of the plurality ofsubstantially discrete gear ratios of the continuously variabletransmission occurs.
 17. The method according to claim 14, furthercomprising the step of controlling the prime mover controller to reducethe torque output of the prime mover.
 18. The method according to claim14, further comprising the step of controlling the prime movercontroller to increase the torque output of the prime mover.
 19. Themethod according to claim 14, further comprising the step of controllingthe prime mover controller to raise the torque output of the prime moverat an end of a shift between the plurality of substantially discretegear ratios of the continuously variable transmission.
 20. The methodaccording to claim 14, further comprising the step of controlling theprime mover controller to reduce the torque output of the prime mover atan end of a shift between the plurality of substantially discrete gearratios of the continuously variable transmission.
 21. The methodaccording to claim 14, further comprising the step of providing theprime mover controller with a mechanism for altering the torque outputof the prime mover for an entire duration of the shift between theplurality of substantially discrete gear ratios of the continuouslyvariable transmission.
 22. The method according to claim 14, furthercomprising the step of using an engine as the prime mover and connectingthe prime mover controller to a valve of the engine for altering thetorque output of the prime mover by varying a supply of fuel to theengine.
 23. The method according to claim 14, further comprising thestep of using an electrical motor as the prime mover and connecting theprime mover controller to an electrical supply for altering the torqueoutput of the electrical motor by varying the electrical supply to theelectrical motor.
 24. A transmission control system for a vehicle havinga prime mover connected to a continuously variable transmission, theprime mover supplying a torque output to the continuously variabletransmission and the continuously variable transmission receiving thetorque output from the prime mover and driving the vehicle, thetransmission control system comprising: a prime mover controllerconnected to the prime mover for controlling, during both accelerationand deceleration of the vehicle, the torque output of the prime mover;and a transmission controller connected to the continuously variabletransmission for controlling the continuously variable transmission tooperate, during operation of the vehicle, at a desired one of aplurality of substantially discrete gear ratios of the continuouslyvariable transmission and for controlling shifting of the continuouslyvariable transmission between the plurality of substantially discretegear ratios of the continuously variable transmission; the transmissioncontroller provides a shift signal to the prime mover controllerindicative of a shift between two gear ratios of the plurality ofsubstantially discrete gear ratios of the continuously variabletransmission, the prime mover controller, upon receipt of the shiftsignal, temporarily alters the torque output of the primer mover, and anoperator of the vehicle perceives a feedback signal, indicative of theshift between two gear ratios of the plurality of substantially discretegear ratios of the continuously variable transmission, in the form of asubstantially stepped change in torque output of the prime mover; andwherein the prime mover controller alters the torque output of the primemover by increasing the torque output.
 25. A transmission control systemfor a vehicle having a prime mover connected to a continuously variabletransmission, the prime mover supplying a torque output having asubstantially constant rate of change to the continuously variabletransmission and the continuously variable transmission receiving thetorque output from the prime mover and driving the vehicle, thetransmission control system comprising: a prime mover controllerconnected to the prime mover for controlling, during both accelerationand deceleration of the vehicle, the torque output of the prime mover;and a transmission controller connected to the continuously variabletransmission for controlling the continuously variable transmission tooperate, during operation of the vehicle, at a desired one of aplurality of substantially discrete gear ratios of the continuouslyvariable transmission and for controlling shifting of the continuouslyvariable transmission between the plurality of substantially discretegear ratios of the continuously variable transmission; wherein thetransmission controller provides a shift signal to the prime movercontroller indicative of a shift between two gear ratios of theplurality of substantially discrete gear ratios of the continuouslyvariable transmission, the prime mover controller, upon receipt of theshift signal, temporarily alters the torque output of the primer mover,and an operator of the vehicle perceives a feedback signal, indicativeof the shift between two gear ratios of the plurality of substantiallydiscrete gear ratios of the continuously variable transmission, in theform of an increase in the rate of change in the torque output suppliedby the prime mover.